34 HYATT ON THE TERTIARY SPECIES 



White Jura, A and B included. Prof. Quenstedt and Prof. Fraas have given minute 

 descriptions of the geology, and the map accompanying the official report of the latter to 

 the government of Wurtemburg, is here reproduced with certain essential changes in 

 order to illustrate this description. Though differing with regard to the structure of the 

 underlying portions of the central hill or Cloisterberg, these investigators and Prof. Sand- 

 berger agree in considering the valley to be due primarily to a synclinal depression of the 

 White or Upper Jura, which is the surface rock of the larger portion of the surrounding 

 and more elevated parts of the Alb. 



According to this view then, we start in our history with a more or less closed kettle 

 shaped valley in which the Tertiary rocks, clays and sands, which form the subject of this 

 memoir, were deposited. These belong, according to all authorities, to the Miocene, and 

 according to Sandberger to the upper part of that formation. 



Surrounding the entire edge or rim of the kettle is found a peculiar coarse breccia of the 

 older or Jurassic rocks, cemented together by freshwater limestone. My visits to these 

 rocks were directed wholly to the search for the beds described by Hilgendorf as contain- 

 ing PL aequiumbilicatus and its descendants, and therefore, the geological observations 

 made were merely incidental. I first endeavored to find these rocks as directed by 

 Hilgendorf on the west side of the basin, but did not succeed on account of the stormy 

 weather and my uncertainty as to their exact position. Subsequently, and also in the face 

 of a cold storm, I succeeded in finding two of the formations described by Fraas as occiu'r- 

 ing upon the Burgstall south of Sontheim, or " Die Landzunge zwischen dem Stubenthal 

 und Steinheimer Thai." Prof. Fraas writes of this locality very fully, and the cursory 

 observations made by me accord precisely with his descriptions. The Coarse Breccia lying 

 externally, or next to the Jurassic rocks, I did not visit, but found the Coarse Fresh-water 

 Limestone of Fraas in place. This rests immediately upon and passes into the coarser and 

 underlying Breccia, and contained only poorly preserved fossils, but by careful comparison 

 I have been able to ascertain that they unquestionably belong to the oxystomus series. 

 The natural sections which are abundant leave no room for doubt that the larger number 

 of the forms have a deeper upper umbilicus than is common even in PI. '"'^uuS'''', and 

 approximate more closely to the typical form of PI. oxystomus. There are also several 

 moulds of PI. oxysSus- The umbilicus is large above and deep, as in that species, and the 

 upper ridge and sulcations plainly though slightly marked. 



A fossil somewhat better preserved than others, showed in section a curious 

 intermingling of characteristics. The last part of the outer whorl had the angular aspect 

 of PI. levis Klein as figured by Sandberger. The front part of the same whorl was of 

 somewhat blunter aspect, like PI. levis, as figured by Klein, the size being also about that 

 of the specimen figured by Klein. The upper umbilicus was much shallower than in PI 

 oxystomus, and the lower umbilicus wider. In fact it seemed to be a form combining 

 characteristics of PI. levis, PI. Steinheimensis, and PI. oxystomus. This specimen leads 

 to the supposition that PI. Steinheimensis should be regarded as a variety of PI. levis, a 

 view sustained by Hilgendorf 's observations, and by fifteen authentic specimens of PI. 

 levis received through the kindness of Prof Sandberger. They were collected at Undorf, 

 near Regensburg, and contain several marked varieties. 



